The Impressive Features of Swarming Motility on Antibiotics Resistance

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J DOI: 10.4172/2155-9538.1000224 ISSN: 2155-9538 Bioengineering & Biomedical Science

Review Article Open Access The Impressive Features of Swarming Motility on Antibiotics Resistance Amina M1*and Ahmed B2 1Department of Biology, University of Mustapha Stambouli, Mascara, Algeria 2Department of Biology, University of Oran (Es-senia), Oran, Algeria *Corresponding author: Amina M, Department of Biology, University of Mustapha Stambouli, Mascara, Algeria, Tel: 213-45-804169; E-mail: [email protected] Received date: March 18, 2017; Accepted date: April 15, 2017; Published date: April 20, 2017 Copyright: © 2017 Amina M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

Abstract

Swarming motility is one of the most impressive features of microbial life and requires an extended investigations. Till now days, many studies have indicated that swarming is the most complex type of bacterial motility. It roles include the colonization of hydrated-viscous surfaces, the formation of biofilms and antibiotics resistance. Furthermore, among the human pathogene microbiota, Pseudomonas aeruginosa have attracted a significant interest because of their complexes swarming pattern. The direction of this movement is biased by chemotactic responses to several stimuli. Thus, the present review is focused on Pseudomonas aeruginosa swarming and their exhibition of adaptive antibiotics resistance.

Keywords: Swarming; Motility; Pseudomonas aeruginosa; movement over a semi-solid surface resulting from intercellular Antibiotics resistance interactions and morphological differentiation. A striking feature of swarming motility is the complex fractal-like patterns displayed by Introduction migrating bacteria while they move away from their inoculation point. P. aeruginosa is the most common pathogen isolated from To the best of our knowledge, a review of the literature suggests that hospitalized patients and is a frequent cause of nosocomial infections the first case of tendril-tendril communication was reported by such as pneumonia, urinary tract infections (UTIs), and bacteremia. O’Toole et al. [11] working with P. aeruginosa. This complex type of Nevertheless, attempts of treatment of P. aeruginosa from patients motility is usually defined as a rapid and coordinated translocation of a through intense antimicrobial therapy may lead to significant selection bacterial population across a semi-solid surface [12]. To our of resistance strains in care units of the hospitals [1]. Furthermore, knowledge, the tendril-tendril communications are more related to the Pseudomonas aeruginosa are opportunistic pathogens often associated swarming pattern. Furthermore, bacterial swarming motility has been with gastrointestinal infections, dermatitis, bacteremia, and a variety of shown to be important to formation [13], where cells act not as systemic infections, particularly in patients with severe burns, cancer individuals, but as coordinated groups to move across surfaces, often and AIDS [2]. within a thin-liquid film [14]. Pseudomonas aeruginosa is a major nosocomial pathogen The swarming communities of P. aeruginosa represent a complex representing a critical threat for human health [3] because of its intersection of physical, biological, and chemical phenomena. tolerance and rapid development of resistance towards almost all However, the branched tendril patterns that are often, but not always, current antimicrobial therapies [4]. Moreover, its survival in the host in observed in P. aeruginosa swarms [15,16] require production of the early stages of infection is supported by the secretion of toxins and rhamnolipid (RL) [17] witch reduce surface tension in bacterial virulence factors, including pyocyanin and its proteases elastase and suspensions. In addition to RL, a functional bacterial flagellum is also alkaline protease (AprA) [5,6]. Thus, infections by P. aeruginosa are required for swarms to form tendrils [12]. notoriously difficult to treat because of its acquired resistance to Kohler et al. [16] reported that in addition to flagella, swarming of P. antibiotics. All known mechanisms of antibiotics resistances can be aeruginosa requires the release of two exoproducts, rhamnolipids displayed by this bacterium (intrinsic, acquired, and adaptive); (RLs) and 3-(3-hydroxyalkanoyloxy) alkanoic acids (HAAs), which act sometimes all within the same isolate [3]. It is not surprising that these as wetting agents and chemotactic-like stimuli. According to Du et al. ubiquitous, Gram-negative aerobic rods with polar, monotrichous [17] P. aeruginosa uses the surfactant RL to control physical forces flagella and protein structures on the surface (pili) are responsible for needed by swarms to efficiently expand over surfaces as a thin liquid adherence to respiratory epithelium [7]. Its adaptability and high film. Although it is well known that biological organisms respond to intrinsic antibiotic resistance enable it to survive in a wide range of environmental cues, these swarming bacteria respond actively to alter other natural and artificial settings, including surfaces in medical their environment on a short timescale to greatly improve their facilities [8]. With a defined adherence, motility and biofilm formation, colonization rate. host colonization is made. Biofilms are responsible for antimicrobial resistance [9] and persistent infections [10]. A role for swarming motility during in vivo infection or colonization has not been established. However, transposon insertions It is also noteworthy that, the bacterium Pseudomonas aeruginosa is that attenuate P. aeruginosa virulence in a rat chronic pulmonary capable of three types of motilities: swimming, twitching and infection model map to genes required for swarming [18]. Several cues swarming. The latter is characterized by a fast and coordinated group required for swarming in vitro, namely rhamnolipids and elevated

J Bioengineer & Biomedical Sci, an open access journal Volume 7 • Issue 2 • 1000224 ISSN: 2155-9538 Citation: Amina M, Ahmed B (2017) The Impressive Features of Swarming Motility on Antibiotics Resistance. J Bioengineer & Biomedical Sci 7: 224. doi:10.4172/2155-9538.1000224

Page 2 of 5 glutamate levels are present in the sputum of cystic fibrosis (CF) among microorganisms of a given class, and not produced by the host. patients [19]. Host recognition of PAMPs may have two entirely different consequences. An appropriate response leads to the eradication of a Pseudomonas aeruginosa and Host Defenses microorganism [26]. Many bacteria are capable of forming biofilms, and Pseudomonas These PAMPs are recognized by receptors on phagocytic cells called aeruginosa is one of the most commonly studied. Recent work has pattern recognition receptors (PRRs) and more specifically the tool like begun to uncover some of the genetic and molecular mechanisms receptor. In the case of P. aeruginosa the most well-known examples of underlying biofilms production by this organism. Furthermore, PAMPs are the lipopolysaccharide (LPS) of Gram-negative bacteria. biofilm-growing bacteria cause chronic infections [20] characterized These and other PAMPs are recognized by receptors on phagocytic by persistent inflammation and tissue damage [21]. cells called pattern recognition receptors (PRRs). Because PAMPs are produced only by microorganisms, they are perceived by the Chronic infections, including foreign-body infections, are infections phagocytic cells of the innate immune system as molecular signatures that (i) persist despite antibiotic therapy and the innate and adaptive of infection. immune and inflammatory responses of the host and (ii) in contrast to colonization, are characterized by immune response and persisting Outer membrane lipoproteins, LPS, flagellin, and nucleic acids all pathology. In a static system, during the early stages of biofilm serve as ligands for TLR2, -4, -5, and -9, respectively. These TLRs and development P. aeruginosa cells deficient in flagellar motility exhibit their respective downstream effectors molecules have proven critical to poor surface attachment, while cells lacking type IV pili are unable to the host response to P. aeruginosa, although the protective effects of form microcolonies [22]. TLRs may be impaired and in some cases, enhanced in the CF patient, contributing to the particular susceptibility of individuals with this The single polar flagellum of P. aeruginosa contributes to its disease to P. aeruginosa infection [27]. nomadic lifestyle by exploring new niches in order to colonize and establish biofilms, since the flagellum dictates initial surface In P. aeruginosa, one other possible TLR ligand is flagellin, the interactions [22]. known TLR5 ligand, which has been implicated in a pathogenic role in acute pneumonia [28] and which has been demonstrated to cause Procaryotic flagella operate differently from eucaryotic flagella. The inflammation when instilled into the lungs [29]. As reported in the filament is in the shape of a rigid helix, and the cell moves when this scientific literature, the studies of TLR-Pseudomonas interactions have helix rotates. Considerable evidence shows that flagella act just like been limited to acute infections. Certain of these interactions may fail propellers on a boat [23]. Furthermore, the direction of flagellar to control the infection because of microbial factors (virulent such as rotation determines the nature of bacterial movement, for formation of biofilm and EPS. Pseudomonas monotrichous polar flagella rotate counterclockwise (when viewed from outside the cell) during normal forward Furthermore, Worgall et al. [30] analyzed the capacity of PA to movement, whereas the cell itself rotates slowly clockwise. induce cell death in human alveolar macrophages (AM) and murine dendritic cells (DC), antigen presenting cells that play a central role in The rotating helical flagellar filament thrusts the cell forward in a the initiation of pulmonary host defenses against pathogens. run with the flagellum trailing behind. For a few seconds, the bacterium will travel in a straight or slightly curved line called a run. It is of interest that phagocytes are important in resistance to When a bacterium is running, its flagella are organized into a Pseudomonas infections. Antibodies to somatic antigens and exotoxins coordinated, corkscrew-shaped bundle. Then the flagella “fly apart” also contribute to recovery. Humoral immunity is normally the and the bacterium will stop and tumble. The tumble results in the primary immune mechanism against Pseudomonas infection but does random reorientation of the bacterium so that it often is facing in a not seem to resolve infection in certain patients despite high levels of different direction. Therefore when it begins the next run, it usually circulating antibodies. goes in a different direction [23]. Swarming Motility and Antibiotics Resistance Bacteria lacking flagella caused less inflammation and death than wild-type counterparts in a murine model of acute pneumonia [24], Swarming is one of the two important systems of bacterial motility possibly a reflection of flagellin’s ability to trigger pro-inflammatory and probably related with the pathogenic process in certain host responses via Toll-like receptor 5 rather than to a loss of motility pathologies. An elevated resistance to multiple antibiotics has been per se [25]. reported for swarming populations of many bacterial species in the case of Salmonella enterica [31], Pseudomonas aeruginosa [32], and a To our knowledge, P. aeruginosa is one of the large component of variety of other medium-agar swarmers, including Serratia marcescens the normal microbiota (outer ear, large intestine), in some stress and Bacillus subtilis [33]. conditions, malnutrition, immune deficiency, it become pathogenic and escape to immune system via a specific strategy. For the purpose of this review, our attention will be focused on swarming motility. Swarming allows a colony to migrate collectively It is interesting to point out, that the innate immune system over soft agar surfaces and travel distances that are several orders of distinguishes and recognizes SELF from microbial non-SELF via a set magnitude longer than their cell length within a few hours. P. of specific and non-specific receptors. This recognition (non-specific aeruginosa swarms can have flat, two-dimensional (2D) branches that immunity) strategy is based on the detection of conserved molecular are approximately 2–5 mm wide and less than 1mm thick, with structures that occur in patterns and are the essential products of branching points typically approximately 1 cm from each other [34]. normal microbial physiology. When the effect of antibiotics in these motility types was explored, These invariant structures are called Pathogen-Associated clear differences were observed among the different antibacterial as Molecular Patterns (PAMPs) (unique to microorganisms), invariant

Page 3 of 5 reported by Linares et al. [35]. These authors did not detect any effect movement, confers an added advantage, making swarming an effective on motility in the case of bacteria growing in the presence of strategy for prevailing against antimicrobials. tetracycline, whereas a reduction in both types of motility was observed in the case of ciprofloxacin. Noteworthy, the aminoglycoside Overview the Branched Tendril Patterns of P. tobramycin induced both swimming and swarming of P. aeruginosa. aeruginosa Again, this finding indicates that sub-inhibitory antibiotic concentrations do not necessarily produce a burden on bacterial P. aeruginosa is not a multicellular organism but has social traits physiology but in some occasions may enhance some potentially resembling multi-cellularity, such as biofilm formation [11,40], cell-to- adaptive characteristics useful for colonization of specific cell communication [41] and swarming motility [17,42]. Thus, environments [35]. swarming communities of P. aeruginosa represent a complex intersection of physical, biological, and chemical phenomena [18]. The branched tendril patterns that are often, but not always, observed in P. aeruginosa swarms [16] require production of rhamnolipid (RL) [17]. In addition to RL, a functional bacterial flagellum is also required for swarms to form tendrils [12]. Thus, bacterial swarming motility has been shown to be important to biofilm formation [43,44] and lifecycle (Figure 2), where cells act not as individuals, but as coordinated groups to move across surfaces, often within a thin-liquid film [15].

Figure 1: Macroscopic views of swarming phenotype of P. aeruginosa inoculated on Mueller-Hinton agar (a) and on tryptic soy agar (TSA) (b) and in the presence of oxacillin and cefazolin. Swarming expression is dependent on the microbial medium.

It is also noteworthy in our ongoing study that a branched tendril pattern was observed in the case of Oxacillin and Cefazolin with a resistance phenotype (Figure 1). Thus, and consistent with these observations a question remains open if the branched tendril pattern is induced by the presence of certain class of antibiotics. Figure 2: Biofilm lifecycle occurs in several stages, comprising the The data presented in Drenkard and Ausubel [36] investigations initial attachment where bacteria adhere via Brownian motion, indicate that P. aeruginosa is capable of undergoing transient flagella-driven motility and physiochemical attraction (van der phenotypic changes, which allow the bacteria to increase their Waals interactions). During stage 2-3, reversible and irreversible antibiotic resistance both in vitro and in vivo. attachment, Flagella and Fimbriae permanently anchor the bacteria to the surface. During stage 4, biofilm maturation through cell These authors speculate that resistant phenotypic variants present in division and an extracellular matrix composed primarily of P. aeruginosa biofilms are responsible for the increased resistance to polysaccharides holds the biofilm together. During stage 5, antimicrobial agents observed in CF infections by P. aeruginosa. dispersal, the biofilm matrix is partly broken down and returns to However, Mah and O’Toole [37] found that phenotypes in PA14 RSCV planktonic phase, some bacteria escape to colonize another surface have been associated with the emergence of antibiotic resistance in [42]. bacterial biofilms. The same authors propose that variant phenotypes selected inside mature biofilms by antibiotic treatment and other conditions present in the lung of CF patients or in the biofilm itself (such as nutrient limitation) constitute the so-called resistant biofilm Conclusion phenotype. Another line of research is devoted to understand the link between It seems that the appearance of phenotypic variants in response to swarming patterns motility and antibiotics resistance. To improve antibiotic treatment has been reported in both Gram-negative and upon the current situation, attempts are being made to grasp the Gram-positive bacteria as reported by McNamara and Proctor [38] complex kind of motility where certain species of Pseudomonas data. Butler et al. [39] reported that the analysis of this swarming maintain high cell density circulating within the multilayered colony to motility has revealed the protective power of high cell densities to minimize exposure to antibiotics. Exploring the molecular interactions withstand exposure to otherwise lethal antibiotic concentrations. These may eventually lead to novel strategies to control Immune dysfunction, authors find that high densities promote bacterial survival, even in a infections induced by this bacteria and answer to antibiotic therapy. non-swarming state, but that the ability to move, as well as the speed of

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J Bioengineer & Biomedical Sci, an open access journal Volume 7 • Issue 2 • 1000224 ISSN: 2155-9538